<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        #div1 div{
            color: red;
        }
    </style>
</head>
<body>
<div id="div1">
    <p id="p1">第一个p</p>
    <div>儿子div</div>
    <div>
        <p>孙子p</p>
        <p>孙子p</p>
        <div>孙子div</div>
    </div>
    <p>儿子p</p>
    <p>儿p</p>
</div>
</body>
</html>